WO2002021661A1 - Island network and method for operation of an island network - Google Patents

Abstract

The invention relates to an island network with at least one energy generator, using regenerative energy sources, whereby the energy generator is preferably a wind energy plant with a first synchronous generator, a DC link, at least one first power rectifier and a power inverter, a second synchronous generator and an internal combustion engine which may be coupled with the second synchronous generator. A fully controllable wind energy unit (10) and an electromagnetic coupling (34) between the second synchronous generator (32) and the internal combustion engine (30) are provided in order to establish an island network in which the internal combustion engine can be switched off completely, so long as the wind energy unit is generating enough power for all connected users with an efficiency which is as high as possible.

Description

 Off-grid and method for operating an off-grid

The present invention relates to an electrical island network with at least one energy generator which is coupled to a first generator. Furthermore, a second generator is provided which can be coupled to an internal combustion engine. In such island grids, the energy generator that is connected to the first generator is often a regenerative energy generator, such as a wind turbine, a hydropower plant, etc.

Such island grids are generally known and are used in particular to supply power to areas which are not connected to a central power supply network, but in which regenerative energy sources such as wind and / or sun and / or hydropower, among others, are available. These can be islands, for example, or remote or difficult-to-access areas with special features in terms of size, location and / or weather conditions. However, electricity, water and heat supply is also required in such areas. The energy required for this, at least the electrical energy, is provided and distributed by the island grid. This requires modern electrically operated Devices for proper functioning, however, compliance with relatively narrow limits in the event of voltage and / or frequency fluctuations in the island grid.

In order to be able to comply with these limit values, so-called wind-diesel systems are used, in which a wind energy installation is used as the primary energy source. The AC voltage generated by the wind turbine is rectified and then converted into an AC voltage with the required grid frequency using an inverter. In this way, a grid frequency that is independent of the speed of the generator of the wind energy installation and thus of its frequency is generated.

The grid frequency is therefore determined by the inverter. There are two different versions available. One variant is a so-called self-commutated inverter, which is itself able to generate a stable grid frequency. However, such self-commutated inverters require a high level of technical complexity and are correspondingly expensive. An alternative variant to self-commutated inverters are grid-guided inverters, which synchronize the frequency of their output voltage with an existing grid. Such inverters are considerably cheaper than self-commutated inverters, but always require a network with which they can synchronize. For this reason, a grid generator must always be available for a grid-controlled inverter that provides the manipulated variables required for grid control of the inverter. In known island networks, such a network generator is, for example, a synchronous generator which is driven by an internal combustion engine (diesel engine).

This means that the internal combustion engine has to run continuously to drive the synchronous generator as a network generator. This is also disadvantageous from the point of view of maintenance requirements, fuel consumption and pollution of the environment with exhaust gases, because even if the internal combustion engine only uses a fraction of its available power to drive the generator as a network generator Must provide - the power is often only 3 to 5 kW - the fuel consumption is not insignificant and is at several liters of fuel per hour.

Another problem with known island grids is that there must be so-called "dump loads" reactive loads that consume excess electrical energy generated by the primary energy generator so that the primary energy generator does not enter idle mode when consumers are switched off, which in turn leads to mechanical operation Damage to the primary energy generator can result from a too high speed. This is very problematic in particular in the case of wind energy plants as primary energy producers.

The invention has for its object to avoid the aforementioned disadvantages and to improve the efficiency of an island network.

The object is achieved according to the invention with an electrical island network with the feature according to claims 1 and 1 6 and with a method for operating control of an island network according to claim 1 8. Advantageous further developments are described in the subclaims.

The invention is based on the knowledge that the second generator, which has the function of the network generator, can also be driven with the electrical energy of the primary energy generator (wind energy installation), so that the internal combustion engine can be switched off completely and decoupled from the second generator. In this case, the second generator is no longer in the generator, but in engine operation, the electrical energy required for this being supplied by the primary energy generator or its generator. If the clutch between the second generator and the internal combustion engine is an electromagnetic clutch, this clutch can be actuated by applying electrical energy to the primary energy generator or its generator. If the electrical energy at the coupling is switched off, the coupling is disconnected. The second generator is then, as described above, supplied with electrical energy from the primary energy generator and driven (engine operation) when the internal combustion engine is switched off, so that the network generator remains in operation despite the internal combustion engine being switched off. As soon as a connection of the internal combustion engine and thus the generator operation of the second generator is required, the internal combustion engine can be started and coupled to the second generator by means of the electrically actuatable clutch in order to drive the latter, so that this second generator provides additional energy for the electrical standby in generator operation can put.

The use of a fully controllable wind turbine makes it possible to dispense with "dump loads", since the wind turbine, due to its complete controllability, that is to say variable speed and variable blade adjustment, is able to generate exactly the power required, so that "disposal" of excess energy is not necessary since the wind turbine generates exactly the power required. Because the wind turbine only generates as much energy as is required in the network (or is required for further charging of intermediate storage), no excess power has to be eliminated uselessly and the overall efficiency of the wind turbine but also of the entire island network is considerably better than when using "dump loads".

In a preferred embodiment of the invention, the wind energy installation contains a synchronous generator, which is followed by an inverter. This inverter consists of a rectifier, a DC link and a frequency converter. If a further energy source providing DC voltage (direct current), for example a photovoltaic element, is formed in the stand-alone grid, it is expedient that such further primary energy generators, such as photovoltaic elements, are connected to the DC voltage intermediate circuit of the inverter, so that the energy of the additional regenerative energy source in the DC voltage intermediate circuit can be fed. This can increase the range of services available from the first primary energy producer. In order to spontaneously compensate for fluctuations in the available power and / or an increased power demand and secondly to be able to use available energy, which is not currently in demand, however, intermediate stores are preferably provided which can store electrical energy and can release it quickly if required. Such storage devices can be, for example, electrochemical storage devices such as accumulators, but also capacitors (caps) or also chemical storage devices such as hydrogen storage devices, in that hydrogen generated by electrolysis with the excess electrical energy is stored. To deliver their electrical energy, such memories are also connected directly or via appropriate charge / discharge circuits to the DC link of the inverter.

Another form of energy storage is the conversion to rotational energy, which is stored in a flywheel. In a preferred development of the invention, this flywheel is coupled to the second synchronous generator and thus also allows the stored energy to be used to drive the network generator.

Electrical energy can be supplied to all stores if the energy consumption in the off-grid is less than the capacity of the primary energy generator, for example the wind turbine. For example, if the primary energy generator is a wind turbine with a nominal output of 1.5 MW or a wind farm with several wind turbines with a nominal output of 1 MW and the wind conditions are such that the primary generator can be operated in nominal operation, even though the power consumption in the stand-alone grid is significantly lower than the nominal output In such an operation (especially at night and in times of low consumption in the island network), the primary energy generator can be operated in such a way that all energy stores are charged (replenished) so that at times when the power consumption of the island network is greater than the range of services offered by the primary energy generator once - under certain circumstances only for a short time - to switch on the energy storage. In a preferred development of the invention, all energy generators and intermediate storage devices, with the exception of the energy components (internal combustion engine, flywheel) connected to the second generator, are connected to a common bus-type configured DC intermediate circuit, which is terminated with a single, network-controlled converter (inverter). A very cost-effective arrangement is created through the use of a single, grid-guided inverter on a DC voltage intermediate circuit.

It is also advantageous if further (redundant) internal combustion engines and third generators (for example synchronous generators) that can be coupled to them are provided, so that when there is a greater demand for power than is available from the regenerative energy producers and storage energy, these are generated by operating the further (redundant) generation systems ,

An embodiment of the invention is explained in more detail below by way of example. Show:

1 shows a basic circuit diagram of an island network according to the invention; 2 shows a variant of the principle shown in FIG. 1; and

Fig. 3 shows a preferred embodiment of an island network according to the invention.

FIG. 1 shows a wind energy installation with a downstream converter, consisting of a rectifier 20, via which the wind energy installation is connected to a DC voltage intermediate circuit 28, and an inverter 24 connected to the output of the DC voltage intermediate circuit 28.

In parallel to the output of the inverter 24, a second synchronous generator 32 is connected, which in turn is connected to an internal combustion engine 30 via an electromagnetic clutch 34. The output lines of the inverter 24 and the second synchronous generator 32 supply the consumers (not shown) with the required energy.

For this purpose, the wind turbine 10 generates the power to supply the consumers. The energy generated by the wind turbine 10 is rectified by the rectifier 20 and fed into the DC voltage intermediate circuit 28.

The inverter 24 generates an AC voltage from the applied DC voltage and feeds it into the stand-alone grid. Since the inverter 24 is preferably designed as a grid-guided inverter for reasons of cost, there is a grid former with which the inverter 24 can synchronize.

This network generator is the second synchronous generator 32. This synchronous generator 32 operates when the internal combustion engine 30 is switched off and operates as a network generator. In this operating mode, the drive energy is electrical energy from the wind energy installation 10. This drive energy for the synchronous generator 32 must also be generated by the wind energy installation 10 as well as the losses of the rectifier 20 and the inverter 24.

In addition to the function as a network generator, the second synchronous generator 32 fulfills further tasks, such as reactive power generation in the network, the supply of short-circuit current, effect as a flicker filter and voltage regulation.

If consumers are switched off and therefore the energy requirement drops, the wind energy installation 10 is controlled in such a way that it generates correspondingly less energy, so that the use of dump loads can be dispensed with.

If the energy requirement of the consumer rises to such an extent that it cannot be covered by the wind energy installation alone, the internal combustion engine 28 can start up and the electromagnetic clutch 34 is subjected to a voltage. As a result, the coupling 34 establishes a mechanical connection between the internal combustion engine 30 and the second synchronous generator 32 and the generator 32 (and network generator) delivers (now in generator mode) the required energy.

A suitable dimensioning of the wind energy installation 10 can achieve that on average sufficient energy from wind energy is provided to supply the consumers. As a result, the use of the internal combustion engine 30 and the associated fuel consumption are reduced to a minimum.

FIG. 2 shows a variant of the island network shown in FIG. 1. The structure corresponds essentially to the solution shown in Figure 1. The difference is that here no internal combustion engine 30 is assigned to the second generator 32, which acts as a network generator. The internal combustion engine 30 is connected to a further, third (synchronous) generator 36, which can be activated if required. The second synchronous generator 32 thus works continuously in motor operation as a network generator, reactive power generator, short-circuit current source, flicker filter and voltage regulator.

A further preferred embodiment of an island network is shown in FIG. In this figure, three wind turbines 10 - which form a wind farm, for example - are shown with first (synchronous) generators, each of which is connected to a rectifier 20. The rectifiers 20 are connected in parallel on the output side and feed the energy generated by the wind energy plants 10 into a DC voltage intermediate circuit 28.

Furthermore, three photovoltaic elements 1 2 are shown, each of which is connected to a step-up converter 22. The output sides of the boost converter 22 are also connected in parallel to the DC voltage intermediate circuit 28.

Furthermore, an accumulator block 14 is shown, which stands symbolically for an intermediate store. In addition to an electrochemical The storage such as the accumulator 14 may be a chemical storage such as a hydrogen storage (not shown). For example, the hydrogen storage can be charged with hydrogen, which is obtained by electrolysis.

In addition, a capacitor block 1 8 is shown, which shows the possibility of using suitable capacitors as a buffer. These capacitors can be, for example, so-called ultra-caps from Siemens, which are characterized by low losses in addition to a high storage capacity.

Accumulator block 14 and capacitor block 18 (both blocks can also be of multiple design) are each connected to DC link 28 via charging / discharging circuits 26. The DC voltage intermediate circuit 28 is terminated with a (single) inverter 24 (or a plurality of inverters connected in parallel), the inverter 24 preferably being designed to be network-based.

A distribution 40 (possibly with a transformer) is connected to the output side of the inverter 24 and is supplied with the mains voltage by the inverter 24. A second synchronous generator 32 is also connected to the output side of the inverter 24. This synchronous generator 32 is the network generator, reactive power and short-circuit current generator, flicker filter and voltage regulator of the island network.

A flywheel 16 is coupled to the second synchronous generator 32. This flywheel 16 is also an intermediate store and can store energy, for example, during the motor operation of the network generator.

In addition, an internal combustion engine 30 and an electromagnetic clutch 34 can be assigned to the second synchronous generator 32, which drive the generator 32 and operate in generator mode if the power from regenerative energy sources is too low. In this way, missing energy can be fed into the island grid. The internal combustion engine 30 assigned to the second synchronous generator 32 and the electromagnetic clutch 34 are shown in dashed lines to illustrate that the second synchronous generator 32 can alternatively only be used in engine operation (and possibly with a flywheel as a buffer) as a network generator, reactive power generator, short-circuit current source, flicker filter and Voltage regulation can be operated.

In particular if the second synchronous generator 32 is provided without an internal combustion engine 30, a third synchronous generator 36 with an internal combustion engine can be provided in order to compensate for a longer-lasting power gap. This third synchronous generator 36 can be separated from the island grid in the idle state by a switching device 44 so as not to burden the island grid as an additional energy consumer.

Finally, a / p / computer) controller 42 is provided, which controls the individual components of the island network and thus permits largely automated operation of the island network.

By means of a suitable design of the individual components of the island grid, it can be achieved that the wind energy plants 10 on average provide sufficient energy for the consumers. This energy supply may be supplemented by the photovoltaic elements.

If the range of services offered by the wind turbines 10 and / or the photovoltaic elements 1 2 is less / greater than the needs of the consumers, the intermediate stores 14, 1 6, 18 can be used (discharged / loaded) in order to either provide the missing power (discharge) or the to store (charge) excess energy. The intermediate stores 14, 1 6, 1 8 smooth out the constantly fluctuating supply of renewable energies.

It is important in terms of the storage capacity of the intermediate stores 14, 1 6, 1 8 depending on the period over which which fluctuation in performance can be compensated. With a generous dimensioning of the intermediate storage, a period of time from a few hours to a few days can be considered.

Only when there are performance gaps that exceed the capacities of the intermediate stores 14, 1 6, 1 8, it is necessary to connect the internal combustion engines 30 and the second or third synchronous generators 32, 36.

In the above description of the exemplary embodiments, the primary energy generator is always one that uses a regenerative energy source, such as, for example, wind or sun (light). However, the primary energy generator can also use another renewable energy source, for example hydropower, or can also be a generator that uses fossil fuels.

A seawater desalination plant (not shown) can also be connected to the island grid, so that in times when the consumers on the island grid need significantly less electrical power than the primary energy producers can provide, the seawater desalination plant consumes the "surplus", that is to say still to be provided electrical power, to produce process water / drinking water, which can then be stored in catch basins. If, at certain times, the electrical energy consumption of the island grid is so great that all energy producers are only able to provide this power, the desalination plant will be shut down to a minimum, or even shut down completely. The control of the seawater desalination plant can also take place via the control 42.

In times when the electrical power of the primary energy producers is only partially required by the electrical network, a - also not shown -

Pump storage plant operated by means of water (or other liquid media) from a lower to a higher potential, so that the electrical power of the pumped storage plant can be accessed if necessary. The control of the pumped storage plant can also take place via the control 42.

It is also possible to combine the desalination plant and a pumped storage plant by pumping the process water (drinking water) generated by the desalination plant to a higher level, which can then be used to drive the generators of the pumped storage plant if necessary.

Claims

Expectations 1 . An isolated electrical network with at least one first energy generator, which uses a regenerative energy source, the energy generator preferably being a wind energy installation with a generator, a second generator being provided which can be coupled to an internal combustion engine, characterized by a wind energy installation which is variable in terms of its speed and blade adjustment is adjustable and an electromagnetic clutch between the second generator and the internal combustion engine. 2. Electrical island network according to claim 1, characterized in that the first energy generator has a synchronous generator which contains a converter with a DC voltage intermediate circuit with at least a first rectifier and an inverter. 3. Electrical island network according to claim 1 or 2, characterized by at least one electrical element connected to the DC voltage intermediate circuit for feeding electrical energy with DC voltage. 4. Electrical island network according to claim 3, characterized in that the electrical element is a photovoltaic element and / or a mechanical energy storage and / or an electrochemical storage and / or a capacitor and / or a chemical storage as an electrical buffer. 5. Electrical island network according to one of the preceding claims, characterized by a flywheel which can be coupled to the second or a third generator. 6. Electrical island network according to one of the preceding claims, characterized by a plurality of internal combustion engines, each of which can be coupled to a generator. 7. Electrical island network according to one of the preceding claims, characterized by a controller for controlling the island network. 8. Electrical island network according to one of the preceding claims, characterized by a step-up / step-down converter (22) between the electrical element and the DC voltage intermediate circuit. 9. Electrical island network according to one of the preceding claims, characterized by charging / discharging circuits (26) between the electrical storage element and the DC voltage intermediate circuit. 1 0. Electrical island network according to one of the preceding claims, characterized by a flywheel with a generator and a downstream rectifier (20) for feeding electrical energy into the DC voltage intermediate circuit (28). 1 1. Electrical island network according to one of the preceding claims, characterized in that all energy generators (10, 1 2) and intermediate stores (14, 1 6, 1 8) using regenerative energy sources feed a common DC voltage intermediate circuit. 1 2. Electrical stand-alone grid according to one of the preceding claims, characterized by a grid-controlled inverter. 1 3. Electrical island network according to one of the preceding claims, characterized in that the energy for operating the electromagnetic clutch is provided by an electrical memory and / or by the primary energy generator. 14. Island network according to one of the preceding claims, characterized in that a seawater desalination / industrial water production system is connected to the island network, which generates domestic water (drinking water) when the range of services of the primary energy producers is greater than the power consumption of the other electrical consumers connected to the island network. 1 5. Island network according to one of the preceding claims, characterized in that a pumped storage plant is provided, which receives its electrical energy from the primary energy generator. 1 6. Electrical island network with at least a first primary energy generator for generating electrical energy for an electrical island network, wherein a synchronous generator is provided, which has the function of a network generator, wherein the synchronous generator can work in motor operation and the energy required for motor operation from the primary energy generator Is made available. 1 7. Island grid according to claim 1 6, characterized in that the generator can be connected via a clutch to an internal combustion engine, which is switched off when the electrical power of the primary energy generator is greater or approximately the same as the electrical power consumption in the island grid. 1 8. Method for controlling the operation of an electrical island network with at least one wind energy installation, characterized in that the wind energy installation (10) is controlled in such a way that it always only generates the required electrical power if the consumption of the electrical power in the network is less than the electrical one Power generation capacity of the wind turbine. 1 9. The method according to claim 1 8, characterized in that when the required power falls below the Energy generators (10, 12) using regenerative energy sources are first of all electrical buffers (14, 1 6, 1 8) used for energy delivery. 20. The method according to any one of claims 1 8 and 1 9, characterized in that internal combustion engines are provided for driving at least one second generator, and the internal combustion engines are only switched on when the energy generators (10, 1 2) and used by the regenerative energy sources / or the power output by electrical buffers (14, 1 6, 1 8) falls below a predeterminable threshold value for a predeterminable period of time. 21. A method according to claim 20, characterized in that more energy is generated from regenerative sources for loading the intermediate storage than is required for the consumers on the network. 22. Use of a synchronous generator as a network generator for a network-controlled inverter for feeding an AC voltage into an electrical supply network, the generator operating in motor mode and the generator being driven by a flywheel and / or by the provision of electrical energy from a regenerative energy generator.